Structural health monitoring with ultrasonic phased array structural radar technology has already proved its high potential for damage detection. The advantage of these active-passive phased array SHM technologies is that there is no need to install a plurality of transducers all over the structure to be monitored, but only limited array assemblies at certain localized areas that can inspect wide structure areas without compromising the surface clearance. By proper electronic beam-forming, signal acquisition and image reconstruction algorithms similar to radars or sonar, an ultrasonic image of the wide structure areas or its interior can be obtained. In order to be able to apply this technology efficiently on real structures and in real service environments many additional problems are to be solved first. The first one is a lack of integrated phased array transducer that once installed on the structure, can provide at all moment reliable signal integrity, necessary signal quality and reliability, reliable energy transducing functionalities and carry necessary integrated hardware for structural health monitoring with possibility to disconnect easily on demand. Present SHM systems based on different SHM technologies in general, always, consist of a plurality of transducers or sensors, multiple cables from each one of them connected to a centralized multi channel bulky equipment necessary for generation, sensing, conditioning, amplification, multiplexing, conversion, triggering, processing, signals storage or communication. This centralized SHM hardware is intended to be positioned and fixed in a certain place on board and more or less far away from the sensors/transducers. These kinds of centralized SHM systems of course are not always very attractive to the clients, aircraft manufacturers, operators, maintenance providers or crew cabin. The main reasons are “lots of cables” and associated time and money cost for proper cabling, relation between corresponding induced costs and performance benefits per added SHM system mass, need to assure a special free space on board or moreover need to design and fix additional support structure just for the installation of the bulky SHM equipment, etc. All these reasons make these conventional kinds of SHM systems unfeasible and impracticable (especially in aerospace sector) for SHM applications during manufacturing, curing or assembly which are also considered as critical phases of a structure life cycle and are prone to accidental damages, disbands, over stresses, plasticities, material deteriorations and the like.
From the sensor assembly described in U.S. Pat. No. 7,302,866 by The Boeing Company, it is clear that it is foreseen mainly for SHM on ground applications, on external easy accessible aircraft surfaces and is not envisaged for continuous structural health monitoring. The connection of corresponding SHM system with the sensor is done manually through special interface module taking always care on correct alignments and pressure based electric multi pads contact integrity. Once acquired necessary SHM data, the interface module should be manually disconnected and proceed with the same process to all other phased array sensors. These sensor assembly, SHM system and SHIM methodology still requires substantial manpower implication and are clearly not suitable for continuous real time SHM on structures in real service environments like flight, movements, vibrations, electromagnetic interferences, adverse weather or environmental conditions, etc.
From the sensor network with embedded electronics described in US 2007/0018083 A1 by the Acellent Technologies the concept of distributed electronics for SHM is introduced but the proposed solution still uses cables or wires (not shown) to connect sensors with the electronics or tries to embed this local electronics into a flexible layer without resolving how. The solution to the common connection problem, in order to be able to function in harsh environments, between small delicate transceivers and rigid electronics is not offered. Also from the invention description it seems that there is no possibility to separate electronics from a transducer once embedded into a layer which of course is not very attractive when electronics fails or there is a need to remove it with another one, resulting with need to remove entire layer together with the electronics.
The component evaluation system for SHM disclosed by The Boeing Company within U.S. Pat. No. 7,822,258 B2 comprise a plurality of piezoelectric transducers within the composite structure component, a transceiver circuit, a switch box for coupling analog to digital monitoring hardware, where said monitoring hardware seems to be referred to one central and common personal computer per one switch box and one transceiver circuit. From the proposed structure of this evaluation system it is clear that the system is not foreseen for aircraft lifetime embarking, inspection of entire mobile platform, to monitor plurality of transducers in real time or make possible on board inspection during real structure service. With the proposed evaluation system structure, it seems that mainly on ground inspections and based on monitoring one by one transducer could be performed, once the mobile platform stationary. It also assumes necessary use of cables for connection of transducers and systems components. The problem of reliable and permanent connections of rigid switch box with a plurality of sensitive small transducers is not proposed. The need to embed one or more layers with distributed array of transducers within the composite structure in order to inspect the structure interior does not seem very attractive due to the need to change actual manufacturing processes or certify new ones. Additionally, embedding of distributed layers for sure will change structure or component properties and could be a future potential source of disbonding or damage initiation. In the proposed SHM method for inspection of composite structures image reconstruction is performed on one central computer and directly from received signals.
Efficient SHM systems in general, due to use of many transducers, require very high generation, acquisition, signal conditioning, processing, memory and communication performances in order to offer quality SHM results easy to interpret. In order to apply them extensively on real aerospace structures in the near future and obtain all potential benefits of their use, mass effective, cost effective, functional SHM systems methodologies with great potential for automation have to be developed. Their mass effectiveness per mass of the structure is of special importance knowing that aircraft payload weight or number of aircraft systems on board is continuously increasing putting more and more difficult requirements onto aircraft structures.